Human embryonic stem cells are typically cultured in media that contains basic fibroblast growth factor proteins. The growth factors are usually supplied in the form of fibroblast feeder layers or by the use of fibroblast-conditioned media. Supplementing such media with recombinant growth factors and cytokines helps boost self-renewal and differentiation of both embryonic and induced pluripotent stem cells.
In this regard, Fibroblast Growth Factor-2 (FGF2) is an important component of human embryonic stem cell culture media because it helps maintain the cells in an undifferentiated state. Thus, one function of FGF2 is to prolong the pluripotency period of the cells and, consequently, their ability to differentiate into various different cell types. See Xu C, et al. (2005) Stem Cells 23:315-323. Sufficiently high concentrations of FGF2 permit the culture of human embryonic stem cells in fibroblast unconditioned medium, which does not contain fibroblasts. See Levenstein M E, et al. (2006) Stem Cells 24:568-574.
FGF2 is however more rapidly degraded in fibroblast unconditioned medium than in fibroblast-conditioned medium when incubated with embryonic stem cells for prolonged periods at 37° C. See Levenstein M E, et al. (2006) Stem Cells 24:568-574. Consequently, it is usually necessary to supplement the unconditioned medium with fresh FGF2 on a daily basis, in order to maintain an effective concentration in the culture. The short half-life of FGF2 in culture is of concern in the industry from a cost perspective, especially in the context of manufacturing schemes that employ large-scale cell cultures to produce stem cell-based therapeutics.